Carboxylate esters are produced by a range of procedures which involve reaction mechanisms such as oxidation, disproportionation or dehydrogenation, as directed to reactants such as alcohols, aldehydes, acetals, and the like.
The Tishchenko reaction is illustrative of an early prior art method of ester synthesis. The process involves disproportionation of an aldehyde such as acetaldehyde into the corresponding ester, e.g., ethyl acetate, in the presence of an aluminum alkoxide catalyst.
U.S. Pat. No. 1,869,761 discloses a process for vapor phase conversion of alcohols to esters in the presence of a silver-uranium carbonate catalyst.
U.S. Pat. No. 1,975,853 describes a process for producing ethyl acetate by contacting ethanol in vapor phase under high pressure with a catalyst consisting of metallic copper and a difficultly reducible oxide.
U.S. Pat. No. 2,012,993 proposes the inclusion of water in a reaction mixture of an alcohol and a dehydrogenation catalyst to suppress the formation of higher alcohols and increase the production of ester derivatives.
U.S. Pat. No. 2,504,497 discloses a new type of catalyst for dehydrogenation of alcohols to esters. The catalyst consists of a porous aluminum-copper alloy composition.
U.S. Pat. No. 3,188,330 discloses a liquid phase method for converting alcohols into ketones and esters in the presence of a carboxylic acid salt of a Group IIB metal, e.g., cadmium or zinc.
U.S. Pat. No. 3,287,401 describes the production of esters by the reaction of an alcohol/aldehyde mixture at 200.degree.-600.degree. F. in the presence of a molybdenum-containing catalyst such as sulfided cobalt molybdate.
U.S. Pat. No. 3,452,067 proposes the use of a supported molybdenum sulfide catalyst for dehydrogenation of alcohols to esters in the vapor phase.
U.S. Pat. No. 3,639,449 discloses a process for converting alcohols to esters by reaction with molecular oxygen in the presence of a palladium or rhodium oxide catalyst.
U.S. Pat. No. 3,819,685 describes the preparation of acrylic esters and methacrylic esters by reaction of acrolein or methacrolein with an alcohol and molecular oxygen in the presence of a cobalt-molybdenum type of oxidation catalyst.
U.S. Pat. No. 4,052,424 discloses a process for producing alkyl alkanoate esters which involves contacting a primary alkanol in vapor phase with a silver-cadmium alloy or silver-cadmium-zinc alloy catalyst at 250.degree.-600.degree. C.
There has been a continuing research effort to develop improved catalysts and procedures to overcome the disadvantages of known processes for converting alcohols and/or aldehydes to carboxylate esters. A main disadvantage is the low conversion selectivity to the desired products, and the concomitant formation of major proportions of byproducts such as carbon dioxide and aldol condensates.
Accordingly, it is an object of this invention to provide a one-step vapor phase process for converting an alcohol/aldehyde mixture into carboxylate ester product with high conversion and selectivity. For example, wherein the conversion of aliphatic aldehyde is at least about 90 percent, and the selectivity to ester product is at least about 70 percent based on the aliphatic aldehyde.
It is another object of this invention to provide a novel dehydrogenation catalyst composition which exhibits high selectivity for the conversion of an alcohol/aldehyde mixture via a hemiacetal intermediate to carboxylate ester product.
Other objects and advantages of the present invention shall become apparent from the following description and examples.